Although the hydro-sulphurisation (HDS) processes have dominated the de-sulphurisation of liquid fuels in the past, their cost and the need to decrease the sulphur levels in the composition of gasolines, to a range of 10-100 ppm, have combined to encourage the development of alternate technologies. Various alternate processes for the de-sulphurisation of gasoline and diesel have been explored, such as direct adsorption (Nagi et al. U.S. Pat. No. 4,830,733, 1983), selective oxidation (S. E. Bonde et al. ACS Div. Pet. Chem. Preprints, 44[2], 199, 1998; E. D. Guth et al. U.S. Pat. No. 3,919,405, 1975; J. F. Ford et al. U.S. Pat. No. 3,341,448, 1967) and bio-processing (M. J. Grossman et al. U.S. Pat. No. 5,910,440, 1999; A. P. Borole et al. ACS Div. Pet. Chem. Preprints, 45, 2000).
In the case of the oxidating de-sulphurisation processes (ODS), an economic system is sought that is sufficiently selective to oxidate the sulphur compounds, thus increasing their polarity and molecular weight facilitating their later separation by extraction or distillation. Until this moment, no commercial oxidating de-sulphurisation process has been developed basically due to the combination of regulatory and economic requirements on an industrial scale, although a wide variety thereof exist under development (S. E. Bonde et al. ACS Div. Pet. Chem. Preprints, 45,375, 2000).
The elimination of the sulphur present in the liquid fuels such as sulphurs, di-sulphurs and mercaptans can be performed by means of the use of organic peroxyacids, such as peroxyacetyl acid which allows decreases in the sulphur content of some gasolines of around 95% working at temperatures of between 2 and 100° C. (S. E. Bonde et al. ACS Div. Pet. Chem. Preprints, 44[2], 199, 1998), although peroxysulfuric and peroxoborate acids have also been used (F. Zannikos et al. Fuel Proc. Tech., 42, 33, 1995) and even other inorganic oxidants such as O3 and oxidant species of the O3−2 type generated from these (A. G. Lyapin et al. U.S. Pat. No. 5,824,207, 1998) and Nitrogen oxide E. D. Guth et al. U.S. Pat. No. 3,847,800, 1974 and U.S. Pat. No. 3,919,405, 1975); as well as experiences with the presence of catalysts. Among the latter the following stand out: the use of heteropolyacids of the peroxotungstophospates in two-phase systems, with H2O2 as an oxidant and phase transfer agents, which obtain excellent conversions of mercaptans, dibenzothiophenyls and dibenzothiophenyl substitutes (above 90%), but a poor decrease in thiophene and benzothiophene compounds (F. M. Collins et al. J. Mol. Catal. A:Chem., 117, 397, 1997); the use of solid catalysts, among these the microporous titanosilicates of the TS-1 and TS-2 types, with an excess of the various organic and inorganic oxidants, in liquids that contain Sulphur compounds that achieve low levels of conversion of the corresponding sulfones (T. Kabe JP 11140462 A2, 1999).
In general, the selective oxidation of compounds of the benzothiophene, dibenzothiophene families and their respective alkyl, di-alkyl and tri-alkyl homologue substitutes is problematical and has not been carried out with total success up to the present time. Catalysts of the TS-1 and TS-2 types, based on microporous titanosilicates with a zeolite structure (M. Taramasso et al. U.S. Pat. No. 4,410,501, 1993), permit selective oxidation of different sulphurs with oxygenated water (R. S. Reddy et al. J. Chem. Soc., Chem. Commun., 84, 1992; V. Hulea et al. J. Mol. Catal. A: Chem., 111, 325, 1996); but their small pore opening makes their use in processes wherein much larger molecules are involved impossible, such as the case of the benzothiophenes and the alkyl-benzothiophenes, the main components in the group of compounds with sulphur present in heavy gasoline and diesel cuts.